According to the study, Las Vegas' carbon emission from transportation and residential buildings actually decreased from 2000 to 2005, although the study's authors on Wednesday cautioned that carbon counting methods weren't as thorough in 2000. They urged readers to take that data with a grain of salt.

The study also said the average resident in metropolitan Las Vegas emitted 2.013 metric tons of carbon from highway transportation and residential energy in 2005, compared with 2.24 tons of carbon emitted by the average 100-metro resident and 2.60 tons of carbon emitted by the average American. The average Las Vegas resident emitted 1.032 tons of carbon from highway transportation (rank 9th) - 0.845 tons from autos (rank 12th) and 0.186 tons from trucks (rank 13th) - and 0.981 tons of carbon from residential energy use (rank 33rd).